With regard to some tools it is of great importance that the user applies the tool and works with it in a straight horizontal direction. This is true, for instance, for an electric drill. In order to drill properly a hole into a vertically positioned wall, in most cases the drill bit must be contacted with the wall such that the longitudinal axis of the drill bit is located in a horizontal plane. Any deviation or inclination from the true horizontal direction should be discovered and corrected before the drilling process proper starts. For the user of the drill the determination of such inclination without any indication device may be difficult, in particular when the user cannot standright behind the drill or when the user has to reach to the side or overhead.
Consequently, when the user wants to drill a horizontal hole into a vertical wall by means of an electric drill, the user would like to have a clear indication whether or not a vertical deviation from a strictly horizontal direction prevails, in order to provide for a correction, if necessary.